1. Field of the Invention
The present invention relates to a member having a surface on which a material is less likely to be deposited, more specifically a member having an antifouling surface on which the so-called xe2x80x9cstains,xe2x80x9d such as deposits and contaminants, are less likely to be deposited, and a composition for the production of a member having such a surface. The present invention also relates to a method for imparting, to the surface of a desired member, such a property that a material is less likely to be deposited thereon, more specifically a method for imparting such a property that stains, such as deposits and contaminants, are less likely to be deposited.
2. Background Art
In the field of buildings and coatings, the pollution of the environment has posed a problem of contamination of exterior materials for buildings, outdoor buildings, and coatings provided thereon.
Dust and particles floating in the air deposit on the roof and the outer wall of buildings in fine weather. Upon exposure to rainfall, the deposits flow together with rainwater and flow down along the outer wall of the building. Further, in rainy weather, dust and particles floating in the air are carried by rain and flow down on the outer wall of the building and the surface of the outdoor building. As a result, the contaminant adheres on the surface along the course of the rainwater. As the surface dries, soil appears in a stripe pattern on the surface.
Combustion products, such as carbon black, municipal dust, and contaminants of inorganic materials, such as clay particles, constitute the soil on the coating of the exterior material for the building. Such a wide variety of contaminants are considered to render measures for antifouling complicate (Yoshinori Kitsutaka, xe2x80x9cGaiheki Shiage Zairyou No Osen No Sokushin Shiken Houhou (Accelerated Testing Method for Contamination of Finish Materials of Outer Wall),xe2x80x9d Journal of Structural and Construction Engineering (Transactions of AIJ), No. 404, October 1989, pp. 15-24).
The use of a water-repellent paint, such as polytetrafluoroethylene (PTFE), has hitherto been considered preferable for preventing the exterior of the building and the like from being soiled. In recent years, however, that the surface of the coating is made hydrophilic as much as possible has become recognized as more effective for municipal dust containing a large amount of a hydrophobic component (Kobunshi, Vol. 44, May 1995. p. 307). Accordingly, coating of buildings with a hydrophilic graft polymer has been proposed in a newspaper (xe2x80x9cJapan Chemical Weekxe2x80x9d, Jan. 30, 1995). According to this report, the coating has a hydrophilicity of 30 to 40xc2x0 in terms of contact angle thereof with water.
Inorganic dust typified by clay minerals has a contact angle thereof with water of 20xc2x0 to 50xc2x0 and, hence, has affinity for the graft polymer having a contact angle thereof with water of 30xc2x0 to 40xc2x0 and is likely to adhere on the surface of the graft polymer. Therefore, it is considered that the coating of the graft polymer cannot satisfactorily prevent soiling with inorganic dust.
Although there are proposals wherein the surface of a member is rendered water-repellent or hydrophilic to keep the surface clean, such as those described above, there is still room for improvement in the surface cleaning activity.
The present inventors have now found that a surface having both a hydrophobic portion, and a hydrophilic portion induced by a photocatalyst has a very good antifouling property. The present invention has been made based on such finding.
Accordingly, an object of the present invention is to provide a member having a surface on which a material is less likely to be deposited.
Another object of the present invention is to provide a member having an antifouling surface on which the so-called xe2x80x9cstains,xe2x80x9d such as deposits and contaminants, are less likely to be deposited.
The member according to the present invention has both a hydrophobic portion, and a hydrophilic portion induced by a photocatalyst, the hydrophobic portion and the hydrophilic portion being present in a microscopically dispersed and exposed state on the surface of the member.
According to a first aspect of the present invention, there is provided a member comprising: a substrate; and a surface layer provided on the substrate, the surface layer comprising a photocatalytic oxide, a silicone resin or silica, and a water-repellent fluororesin, the silicone or silica and the water-repellent fluororesin being present in a microscopically dispersed and exposed state on the outermost surface of the surface layer.
According to a second aspect of the present invention, there is provided a member comprising: a substrate; and a surface layer provided on the substrate, the surface layer comprising a hydrophobic resin and a photocatalytic oxide, the hydrophobic resin and the photocatalytic oxide being present in a microscopically dispersed and exposed state on the outermost surface of the member, the photocatalytic oxide being self-hydrophilified or functioning to hydrophilify the photocatalytic oxide still remaining unhydrophilified present around the photocatalytic oxide by photocatalytic action created in response to photoexcitation.
In both the aspects of the present invention, the hydrophobic portion derived from the hydrophobic resin and the hydrophilic portion induced by the photocatalyst are present in a microscopically dispersed state on the outermost surface of the member. As a result of the hydrophobic portion and the hydrophilic portion adjacent to each other, a hydrophilic deposit having affinity for the hydrophilic portion does not have affinity for the adjacent water-repellent portion. On the other hand, a hydrophobic deposit having affinity for the hydrophobic portion does not have affinity for the adjacent hydrophilic portion. Therefore, it is considered that both the hydrophilic deposit and the hydrophobic deposit cannot deposit on the surface of the member, and, even when deposited on the surface of the member, are unstable and hence are easily removed, permitting the surface of the member to be kept clean. In this connection, however, it should be noted that the above description is hypothetical and the present invention is not limited to the above mechanism alone.